| Summary: | 碩士 === 元培科技大學 === 食品科學研究所 === 100 === The prevalence and incidence of Alzheimer's disease (AD) is increasing with aging. One of the mechanisms proposed for Alzheimer’s disease is the formation of advanced glycation end products (AGEs). AGEs are the irreversible products of the maillard reaction between carbohydrates and proteins. By interacting with the receptor for AGEs (RAGEs), AGEs can activate microglia cells to increase the production of various cytokines, such as tumor necrosis factor (TNF-α), interleukin-6 (IL-6), interleukin-1β (IL-1β) and to induce the expression of inflammation-related enzymes such as inducible nitric oxide synthase (iNOS) and thereby, exerts their deleterious inflammatory response.
The present study was to evaluate the inhibitory capacities of several herbal teas on the advanced glycation end-products (AGEs) formation and on the AGEs-induced inflammatory cytokines production in vitro. Twelve herbal teas were selected and extracted with hot water. After freeze-dried, the herbal tea extracts were conducted to evaluate the composition, the antioxidant activity, the anti-glycation capacity and the inhibitory capacity on the AGEs induced inflammation.
The results indicated that green tea and lemon balm containing 302.2 ± 23.0 mg GAE /g and 226.7± 31.5 mg GAE /g of polyphenol, respectively, were rich in total polyphenol. Lemon balm and lemon verbena containing 245.5± 3.5 mg CE /g and 171.6± 4.9 mg CE /g of flavonoid, respectively, were abundant in flavonoid. Green tea and black tea had 16.4±0.3 mg CE /g and 4.3±0.0 mg CE /g of condensed tannin, respectively. However, the condensed tannin content of other tested herbal teas was rare and could not be detected. Four methods, including DPPH radical scavenging, Fe2+ -chelating, oxygen radical absorbance capacity and superoxide anion (O2-．) scavenging, were adopted to measure the antioxidant activity of the herbal teas. The results showed that lemon balm, rose pink and green tea had the best ORAC values of 3.2 mole TE /g, 2.5 mole TE /g and 2.0 mole TE /g, respectively. Similarly, green tea, lemon balm and rose pink had the greatest DPPH radical scavenging and superoxide anion (O2-．) scavenging activities, with an IC50 ranging from 0.1 mg/ml to 1.3 mg/ml. Marigold and sage exhibited the strongest Fe2+-chelating capacity. The IC50 (the concentration which need to chelate 50% of presented Fe2+ ion) values of marigold and sage were 0.4 mg/ml and 0.6 mg/ml, respectively. In the other hand, green tea, black tea, lemon balm and sage had significant capacities to inhibit the fluorescence AGEs formation in an in vitro glucose-mediated protein glycation system. The result indicates that green tea, black tea, lemon balm and sage had potent anti-glycation capacities.
The present study adopted advanced glycation end-products (AGEs) -stimulated inflammation in BV2 microglia as an inflammatory cell model to evaluate the anti-inflammatory effect of the herbal teas. The results showed that all of the 12 tested herbal teas dose-dependently suppressed the production of NO in the AGEs-stimulated BV2 microglia, with an IC50 ranging from 0.2 mg/ml to 4.1 mg/ml. Green tea, lemon verbena, lavender and sage with an IC50 lower than 1 mg/ml, were good at inhibiting NO production. At the testing concentration of 2.5 mg/ml, lemon verbena, rose pink, green tea and sage inhibited more than 80% of AGEs-induced IL-6 production. However, all of the tested herbal teas could not inhibit the AGEs-induced TNF-α production in BV2 microglia cell. Additionally, the mRNA levels of iNOS and IL-6 were highly correlated with NO and IL-6 secreted. This result implied that herbal teas affect the production of NO and IL-6 through regulation on their gene expression. Moreover, significant correlations were existed among the iNOS, IL-6 and IL-1β mRNA levels which implying that herbal teas might affect the convergent upstream transcription factor, the nuclear factor-κB, and therefore, co-regulate the expression of these downstream pro- inflammatory factors.
Collectively, green tea had excellent anti-oxidant and anti-glycating activities as well as potent inhibitory capacity on the AGEs-induced inflammation. In order to find out the possible active components in the green tea, a high performance liquid chromatography (HPLC) analysis was conducted. It was found that EGCG is the major difference component between green tea and black tea. We suggested that EGCG is the major active component responsible for the anti-oxidant, anti-glycation and anti- inflammatory activity of green tea. At least, based on our finding, green tea may be useful as a dietary adjuvant to prevent Alzheimer's disease.
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